Human respiration is an extraordinarily complicated process. Although rhythmic breathing, inhalation and exhalation, is familiar to all of us, the underlying processes that give rise to the observed respiration cycle are complex. In general respiration permits gas exchange between gases in the blood and gases in the environment. In a healthy individual, oxygen is provided to the blood and carbon dioxide, which is a product of metabolic processes in the body, is driven off into the atmosphere. Respiration is subject to both voluntary and involuntary control and several disease processes can have a profound impact on respiration.
A person's respiration is controlled by the autonomic nervous system that integrates inputs from many physiologic sensors such as mechanoreceptors and chemoreceptors. The central nervous system commands the diaphragm and other muscles in the chest as well as in the neck to physically contract and relax thus producing a breath of certain shape and tidal volume. It also acts as a respiratory pacemaker by setting the breathing rate. In a normal sleeping person the next breath is typically initiated substantially immediately after the previous breath is completely exhaled. The term tidal volume refers to the volume of air inspired or expired during a respiratory cycle. Together tidal volume and breathing rate determine minute volume of ventilation that determines the rate at which oxygen is delivered and CO2 is removed from the respiratory system.
The term disordered breathing is used herein to describe a variety of observable respiration patterns that deviate from normal respiration. For example, Cheyne-Stokes respiration (“CSR”) is clinically observed and declared when a patient has bouts of “rapid” and/or “deep” breathing followed by reductions in breathing or apnea-hypopnea. This abnormal pattern of breathing can be seen in patients with strokes, traumatic brain injuries, brain tumors, and congestive heart failure and is usually a result of poor control of blood gas chemistry by the central nervous system.
“Pure” Cheyne-Stokes respiration is also called central sleep apnea by the medical community and is sometimes present with congestive heart failure. However, CSR breathing may be mixed with other respiration disorders that may or may not be related to congestive heart failure or other cardiac disorders.